1. Field of the Invention (Technical Field)
The present invention relates generally to the field of communication processes and devices for hearing and/or speech impaired individuals, and in particular to the field of TTY communications over wireless mobile communication devices.
2. Background Art
Hearing impaired and/or speech impaired individuals rely on a variety of communications devices to communicate. Statutes, such as the Americans with Disabilities Act and the Telecommunications Act, provide that telecommunications service providers and telecommunication device manufacturers enhance communication devices such that hearing and/or speech impaired individuals can communicate effectively over existing telecommunication networks.
Many hearing and/or speech impaired individuals communicate with other individuals over existing landline telephone networks primarily via a Telecommunication Device for the Deaf (TDD), which consists of an alphanumeric keyboard and display, or teletypewriter (TTY), that is connected to the telephone through a modem. When a user enters alphanumeric characters on the TTY, tones corresponding to the characters are transmitted via the modem through the telephone line to a receiving TDD. At the receiving TDD, the tones are received by a second modem and converted back to characters to be read by the receiving party on a TTY. A conversation proceeds by taking turns in real time, where the users type messages back and forth over TDDs.
Each character is transmitted and received via a TTY format, most commonly the Baudot/Weitbrecht (hereafter “Baudot”) tone format. In the Baudot format, transmitted tones include a mark tone of 1,400 Hz and a space tone of 1,800 Hz. Serial sequences of marks and spaces provide five-bit binary numbers representing a limited set of characters, including letters of the alphabet, numerical digits, punctuation marks, and space characters. A typical TTY can support 32 characters as shown in Table 1 below. These five-bit words are transmitted over telephone lines at approximately 45.45 or 50 baud.
TABLE 1FIGS ShiftCCITT StandardCode SignalsInternationalNorth American• Denotes possible currentLTRSTelegraph AlphabetTeletype CommercialStart12345StopShiftNo. 2 Used for TelexKeyboard•••A——••••B??••••C::•••DWho are you?$••E33••••FNote 1!••••GNote 1&•••HNote 1#•••I88••••JBellBell•••••K((•••L))••••M..•••N′,•••O99•••••P00•••Q11•••R44•••S,,••T55••••U77•••••V=:••••W22•••••X//••••Y66•••Z+″•Blank••••••Letters shift (LTRS)•••••Figures shift (FIGS)••Space••Carriage return••Line feed
With the advent of mobile communication devices, such as mobile cellular and satellite telephones, pagers, personal digital assistants (PDAs), and the like (hereafter “mobiles”), the Federal Communications Commission (FCC) requires that every mobile manufactured be capable of communicating TTY 911 emergency calls. In order to facilitate the development of TTY communication over digital wireless communication systems in particular, wireless carriers formed the “TTY Forum” in 1997, participants of which included consumers, representatives from government emergency centers, wireless product manufacturers and service providers, and TTY equipment manufacturers. In response to this directive, mobile manufacturers have provided mobiles with the ability to communicate with TTY devices.
Currently, to communicate TTY data via a mobile, an external TTY device must be connected to the mobile through the mobile audio jack. Once the TTY is connected to the mobile, the mobile is set by the user to operate in TTY mode, so that the mobile will transmit and receive data in the TTY data format. The TTY generates tones based upon alphanumeric characters input by the user. The mobile detects these tones through the audio jack. The tones are then transmitted to the receiving mobile over conventional mobile communication means, typically via wireless radio frequency (rf) transmission. To transmit the Baudot tones, the data is encoded with the appropriate TTY packet data extension so that the telecommunications base station and receiving mobile will interpret the incoming signal as a TTY signal. When a mobile receives a TTY signal, a decoder decodes the signal and sends the data to a tone regenerator. These tones are sent back to a TTY device for decoding and display to the receiving user.
One difficulty with TTY communication over mobiles, expressed by consumer advocates, is that in certain mobiles, direct connection through the audio jack blocks access to the microphone in the mobile preventing the user from efficiently alternating between receiving TTY and speaking during a call. Without some means of switching modes in this circumstance, a voice carry over (VCO) user must disconnect the audio cable every time it is the user's turn to speak. Voice carry over is a form of telecommunications relay service where a person with a hearing disability is able to speak directly to the other user, rather than sending data via a TTY. A communications assistant types the response from the other user back to the person with the hearing disability who reads the response from a TTY.
Another difficulty with connecting a TTY device through the mobile audio jack is that some mobiles do not permit simultaneous connection of the audio jack and the mobile power adapter. The audio jack may be located too close to the access point for the power cord, preventing the TTY user from making a call while the mobile is connected to a power outlet.